The present invention relates to a gearbox for agricultural and industrial vehicles, of the type comprising a double clutch, a plurality of pairs of toothed wheels and a plurality of engaging devices.
That type of gearbox is also generally referred to as a dual clutch or DCT (dual clutch transmission) and an example of a gearbox of this type is described in WO2005/021999.
Those gearboxes allow switching of a plurality of transmission ratios without any interruption of the torque transmitted. Usually, they are composed of two engaged transmission shafts which can be selectively connected by means of respective clutches to the input shaft of the main movement. The two engaged transmission shafts are often arranged coaxially one inside the other; the outermost shaft is therefore hollow and the two actuation clutches are arranged at an end of the gearbox, in the region of the input shaft for main movement.
Therefore, the two shafts are connected to a first and a second partial gearbox, the first of which operates, for example, the odd gear stages (for example, 1, 3, 5, 7) while the second one operates the even gear stages (for example, 2, 4, 6, 8). There is further provided an actuation shaft which is selectively connected by means of a first connection to the first input transmission shaft or by means of a second connection to the second input transmission shaft. When shifting from one gear to the successive higher or lower gear, one of those connections is opened and the other is simultaneously closed so that the drive torque can be transferred without interruption of the traction power from one partial gearbox to the other.
Disadvantages of those solutions with respect to other continuous transmission gearbox architectures involve the greater dimension in terms of length and the structural complexity relative to the construction of hollow shafts rotating at high speeds. In order to contain the axial dimensions of the gearbox, there has been configured a particular arrangement of the actuation shaft and the relevant connections as described in WO2006/084555. That solution allows a reduction in the number of rotation axes of the various components of the gearbox but it is still relatively bulky and has quite a complex construction. Furthermore, that structure, similarly to other known structures, does not allow a simple arrangement of a power take-off, unless the dimensions are sacrificed.
Another transmission of this type is described in U.S. Pat. No. 4,777,837. That transmission is also bulky and requires for operation at least three separate shafts which are spaced apart from each other.
The problem of the dimensions is partially solved by the transmission described in EP2126409, in the name of the same Applicant. However, it would be desirable to obtain a transmission which has dimensions which are further reduced and which is particularly efficient during ploughing operations and transport on roads.